Refrigeration apparatus with variable internal defrost means



E. l... WEST, JR

REFRIGERATI'ON APPARATUS WITH VARABLE INTERVAL DEFRosT MEANS 2 Sheets-Sheet 1 Filed Oct. 25, 1968 Vw #W7 LJ (12o f2 July 7, 1970 E. L. WEST, JR

Filed Oct. 25, 1968 2 Sheets-Sheet 2 y fa M zz United States Patent O l 3,518,841 REFRIGERATION APPARATUS WITH VARIABLE INTERNAL DEFROST MEANS Eugene L. West, Jr., Galesburg, Ill., assigner to Philco- Ford Corporation, Philadelphia, Pa., a corporation of Delaware Filed Oct. 25, 1968, Ser. No. 770,501 Int. Cl. F25d 21/06 U.S. Cl. 62-153 9 Clailns ABSTRACT OF THE DISCLOSURE Refrigeration apparatus of the household refrigerator type includes an evaporator automatically defrostable through the agency of an electric heating element energized at varying time intervals. The variation in time intervals between defrost periods is a function of selective energization and deenergization of a dew point compensator, and may also combine the effects of compressor run time and number of door openings. The dew point compensator comprises an electric heater in the region of the breaker frame of the refrigerator, and energization and `deenergization of the compensator is achieved manually, by the user, according to conditions of relative humidity to which the refrigerator cabinet is subjected. The net effect is the shortening of intervals between defrost periods under conditions such that frost can be expected to accumulate rapidly.

BACKGROUND OF THE INVENTION This invention relates to refrigeration apparatus, and more particularly to improvements in defrosting controls for the refrigeration systems of household refrigerators.

In the refrigeration art, ydefrosting controls range from timers for establishing fixed time intervals between defrost periods to means providing for varied intervals and responsive either to the number of door openings, or to the compressor run time, or to the degree of moisture content of the air, and the like. None of these known systems achieves combinations of defrosting and refrigerating periods conducive to efficient operation of a refrigerator.

The present invention has as its general objective the provision of a simple, inexpensive, and novel control means for integrating the effects of humidity, compressor run time, and number of door openings to achieve variations in time intervals between defrost periods conducive to optimum operation of a household refrigerator.

SUMMARY OF THE INVENTION In achievement of the foregoing as well as other objectives, the invention contemplates provision in a household refrigerator of means for defrosting its evaporator automatically at intervals determined primarily by the humidity content of the ambient air. In further particular accordance with the invention, a defrost-interval timer of otherwise conventional design is combined with means operable to modify its defrosting interval in accordance with the degree of refrigerator usage and the climatic conditions to which it is subjected.

The manner in Iwhich the foregoing and other objectives of the invention may best be achieved will be more clearly understood from a consideration of the following description taken in light of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational showing of a two-compartment household refrigerator embodying the invention, and with the doors removed for convenience of illustration;

FIG. 2 is a vertical section of the refrigerator illus- 3,518,841 Patented July 7, 1970 ICC trated in FIG. l, with the doors in place, and taken generally along the line indicated by arrows 2-2 applied to FIG. `l; and

FIGS. 3, 4, and 5 are schematic diagrams of apparatus for achieving defrost of the refrigerator shown in the preceding gures, in accordance with the invention.

DESCRIPTION OF THE SEVERAL EMBODIMENTS With reference to FIGS. l and 2, a refrigerator cabinet y10, having an outer shell 11 and an inner liner 12 spaced therefrom by suitable thermal insulation 13, comprises an above-freezing food storage compartment 14 and a below-refreezing food storage compartment 15 disposed below the former compartment. A pair of door structures 16 and 17 for the cabinet are provided in accordance with well known practice, as shown in FIG. 2 but omitted from FIG. l for convenience of illustration. Compartments 14 and 15 are dened, in cooperation 'with liner 12, by an insulated partition 18 which extends horizontally within the liner. A breaker frame 19 of conventional construction surrounds the front opening of the cabinet, and bridges the gap between outer shell 11 and inner liner 12.

A conventional refrigerating unit is provided for cooling compartments 14 and 15, and includes an evaporator 21, preferably of the in-and-tube type, arranged in the usual series refrigerant flow circuit with a compressor 22 and a condenser 23 cooled by a fan 27. Also provided is a conventional `cabinet light 29 operable by the usual door switch 30 in series with the light and voltage source V. Of course it will be understood that a second light and switch means therefor may be provided for door 1'7.

Evaporator 21 is positioned vertically within a chamber formed by side wall portions of liner 12 and by a pair of spaced vertically extending partitions 24, 24a spanning the width and height of the below-freezing compartment and spaced forwardly of the rear wall of the liner. A fan 25 is arranged to force air (see broken-line arrows indicative of air flow) from the evaporator chamber into the freezer compartment, and to return the air to the chamber for flow over the evaporator. A portion of the air circulated by evaporator fan 25 is forced upwardly through a central duct 26 extending vertically between the rear wall of the upper liner portion and outer shell 11. This upwardly directed cold air (see solid-line air ow arrows) is discharged from duct 26 into an upper portion of the above-freezing compartment, for flow therethrough and return to the evaporator chamber through laterally spaced air passage means 28 in the region of horizontal partition 18. Evaporator 21 is automatically defrostable, and a drain trough 35 positioned below the evaporator directs defrost water into suitable conduit and disposal pan means 36 in the machine compartment.

With reference further to FIG. 3, an electric heater 31 is positioned in high thermal exchange relation with evaportar 21 (not shown in FIG. 3) and is energizable periodically through the contact 33a of a timer switch 33. `Operation of switch 33 is achieved through a cam follower 38a actuated by a cam 38 driven by the defrost timer motor 32. Switch contact 33a is in series electrical circuit with defrost heater 31, defrost thermostat 34, refrigerator thermostat 37, and a source of voltage V. A heater 39 of lesser wattage than defrost heater 31 is connected in parallel electric circuit with heater 31 and thermostat 34, and is located in the region of trough 35 t0 ensure against freeze-up of defrost water in the trough prior to its tlow into the disposal system. Defrost switch 33 includes a second contact 33b in series electrical circuit with source of voltage V, motor compressor 22, and refrigerator thermostat 37. Condenser fan 27 and evaporator fan 25 are in parallel electric circuit with compressor 22. A dew point compensator heater 41 of conventional electrical resistance type is disposed about the forward portion of cabinet 11 (this heater appears in FIG. 3 only) in the region of breaker frame 19, and is under the control of contact 42a, of a double-pole double-throw Imanual selector switch 42, in series with source of voltage V and heater 41. A user of the refrigerator may operate selector switch 42, conveniently of the pushbutton actuated type as shown also in FIG. 1, to open contact 42a and deenergized the compensator heater 41 under normal weather conditions, i.e., weather characterized by low relative humidity such as is the case in the winter season. Switch 42 may be operated to close contact 42a and energize heater 41 in humid weather, e.g. the summer season, when it is desirable to prevent sweating of the outer surface of the cabinet. The feature of selectivity of operation of the dew point compensator has been found beneficial in that it enhances economy of operation of the refrigerator. The present invention recognizes further advantages to be derived from such selectivity of operation.

In especial accordance with the invention, timer motor 32 is connected in series electrical circuit with the source of voltage V and contact 42b of dew point compensator selector switch 42. Also, timer motor 32 is connected in series electrical circuit with refrigerator thermostat 37, contact 42C of selector switch 42, and the source of voltage V. The construction and arrangement is such that under humid weather conditions, when contacts 42a and 42h of selector switch 42 are closed, heater 41 is energized, and defrost timer motor 32 is energized continuously to provide reduced intervals between defrost periods, with consequent frequent defrosting of the refrigerator. On the other hand, when contacts 42a and 42bf of selector switch 42 are in open position and contact 42C is closed, as is the case for normal weather operation, heater 41 is deenergized, and timer motor 32 is energized through refrigerator thermostat 37 only when compressor 22 is in operation.

A defrosting period is achieved by rotation of the timer ca-m 38 to a position in which the cam follower 38a on timer switch 33 is urged, by resilience of the switch arm, into a reduced radius portion 38b of the cam 38. Timer motor 32 is energized during defrost either through the closed switch of refrigerator thermostat 37 and contact 42e of selector switch 42, or through contact 42b, as the case may be, to drive cam 38 through the defrost period. The defrost period is characterized by the deenergization of motor compressor 22 and energization of defrost heater 31 and trough heater 39. Upon completion of defrosting the temperature of evaporator 21 will rise to a value at which defrost thermostat 34 opens to deenergize heater 31. After a suitable soak period, during which no further heat is applied to the evaporator, the timer motor drives switch 33 into its compressor and fan energizing position under the control of its thermostat 34.

With reference to FIG. 4, a modified embodiment of the invention includes a defrost timer that operates on the heat motor principle to establish periods of refrigeration and defrosting as described above. In combination with this timer are various components identical with those described in the previous embodiment, and which components bear the same reference numerals. Considering FIG. 4 in more detail, door switch 30` and cabinet light 29 are in series electrical circuit with a source of voltage V. Also, a dew point compensator heater 41 is in series electrical circuit with contact 42a of selector switch 42 and the source of voltage V. Motor compressor 22, fan 27 and fan 25 are in parallel electrical circuit with one another and in series circuit with a thermostat 37, contact 133b of timer switch 133, and voltage source V. Defrost heater 31 and its thermostat 34 are in series electrical circuit with contact 133a of timer switch 133, thermostat 37, and source of volatge V, and a trough heater 39 is in parallel circuit with the defrost heater and its thermostat 34. The timer motor includes a resistance heater 132 in series circuit with contact 42b of dew point compensator selector switch 42, source of voltage V and a switch including contacts 132b and 132C. Switch contact 132b is supported on a transversely extending portion of a bimetal element 132a that is in heat exchange relation with heater 132. The bimetal heater 132 also is in a series electrical circuit comprising source of voltage V, switch contact 132b on the extension of element 132a, contact 132C, an electrical resistor 50 contact 42C of selector switch 42, and refrigerator thermostat 37. The operating arm of Switch 133 includes a cam follower 138a engageable with a cam 138 including larger and smaller diameter portions. Cam 138 is driven with a gear 55 meshed with a smaller gear 56 that is driven with a gear 57 concentric with the smaller gear. Gear 57 is driven in step-by-step manner through cyclic energization and deenergization of the bimetal heater 132, as will now be explained. Voltage for such cyclic operation of heater 132 is provided at all times, through the circuits described above, either during defrosting when switch contact 133a is closed in response to cam follower 138e dropping into the smaller diameter portion of cam 138, or during refrigeration when contact 13311 is closed in response to the follower riding on the larger diameter portion of cam 138.

In its rest, or bimetal-heater deenergized position, the end portion of the extension of strip 132a is received between adjacent teeth of gear 57. Contact portion 132a comprises a resilient arm, and also is received in the same gap between the teeth. When bimetal heater 132 is energized in the course of its cyclic operation, bimetal element 132a is caused to lex thereby moving its extension to the left, as indicated by the directional arrow, to turn gear 57 one tooth, or one angular increment. In soI doing, the switch contact 132e is moved out of the gap in the gear to fall, by virtue of its resilience, into the preceding adjacent gap, and out of electrical engagement with contact portion 13212, thereby deenergizing the heater 132. As a result, bimetal strip 132a is cooled, and fiexes to move its extension downwardly a distance equal to one tooth of the gear and into the next succeeding gap occupied by contact portion 132c and preventing retrograde movement of gear 57. As bimetal strip extension 132a moves into the next notch or gap, contact 132b again engages the contact 132C to energize heater 132 and repeat the operation just described.

As gear 57 is driven, gear 56 driven therewith drives gear 55, and consequently drives cam 138. During a refrigeration period cam follower 138a rides on the larger diameter portion of cam 138 to maintain compressor energizing switch 133b` closed. When follower 133a drops into the lesser diameter cam portion, defrost heater 31 is energized through contact 133a and defrost thermostat 34, thereby providing a defrost period. It will be understood that thermostatic switch 37 will be closed upon elevation of the evaporator temperature in provision of a defrost period, whereas it will cycle in provision of a refrigeration period. It will be further understood that although thermostatic switch 37 may fbe open upon initiation of a defrost period by the timer mechanism, it will close upon elevation of the evaporator temperature, due to deenergization of compressor 22, thereby energizing defrost heater 31.

In the embodiment shown in FIG. 4, it will be appreciated that when contacts 42a and 42h of selector switch 42 are closed, to energize heater 41 as will be the case during warm, humid weather, the intervals between defrost periods will be minimal since full voltage is applied to bimetal heater 132 through contact 42b. When selector switch contact 42e is closed upon opening contact 42a to deenergize heater 41 as will be the case during cooler, less humid weather, the intervals between defrost periods will be lengthened because bimetal heater 132 will be energized only while thermostatic switch 37 is closed, and at a reduced voltage due to resistor 50 being placed in series circuit with the bimetal heater by closure of contact 42C.

In either of the embodiments illustrated in FIGS. 4 and 5, defrosting will occur at more frequent intervals during warm, humid weather, and at less frequent intervals during relatively cool, less humid weather.

The modified embodiment of the invention illustrated in FIG. 5 is essentially the same as the embodiment illustrated in FIG. 4, but includes an additional heater 60 coupled in series electrical circuit with door switch and source of voltage V. Heater 60 is in high thermal exchange relation with a bimetal strip 61 including a portion that engages a tooth of gear 57. The construction and arrangement is such that when door 16 is open the switch 30 is closed, energizing cabinet light 29 and heater 60. While heater 60 is energized bimetal element 61 is heated and flexes as indicated by the directional arrows applied thereto, to move the gear 57 one increment. This drives smaller gear 56 meshed with gear 55, thereby moving cam 138 one increment. When the door is closed, switch 30 is opened, deenergizing light 29 and heater 60. Bimetal element 60 therefore is cooled and llexes to a rest position in which it engages the next tooth of gear 57, for subsequent movement of the gear by any of the disclosed means for moving the same.

Thus, in the embodiment of the invention illustrated in FIG. 5, intervals between defrosting are a function of the number of door openings. as well as the relative humidity of the ambient air.

From the foregoing, it will be appreciated that the invention aifords simple, inexpensive, and novel control means for integrating variously the effects of humidity, compressor run time, and number of door openings, to achieve variations in the time intervals between defrost periods conducive to optimum operation of a household refrigerator.

I claim:

1. In refrigeration apparatus including cabinet structure, a defrostable evaporator for cooling the interior of said cabinet structure, means for operating said evaporator cyclically, means for defrosting said evaporator periodically, timer means for establishing the intervals between periods of defrosting and operation of said evaporator, and heater means selectively energizable to prevent condensation of moisture on exterior surface portions of said cabinet structure under ambient atmospheric conditions conducive to condensate formation, selective energization of said last recited means being effective to modify the intervals between defrost periods provided by said timer means.

2. Apparatus according to claim 1 and further characterized by the inclusion of means for modifying the intervals provided by said timer means as a function of operation of said means for operating said evaporator, upon selective deenergization of said heater means.

3. Refrigeration apparatus according to claim 2, and further characterized in that Isaid timer means includes drive motor means operable at a rst predetermined rate, and by the inclusion of means for operating said drive motor means at a second, lesser rate than its predetermined rate in modification of the intervals between defrost periods.

`4. Apparatus according to claim 3, and further characterized in that said drive motor means is of the heat motor type comprising an electrical resistance heater and a bimetal element thermally coupled therewith and serving as the output linkage of said timer means, and in that said means for operating said motor means at the recited different rates comprises an electrical resistor disposable in series electrical circuit with said resistance heater lupon selective deenergization of the recited heater means.

5. Refrigeration apparatus according to claim 1, and further characterized by the inclusion of door means for said cabinet structure, door switch -means operable in response to opening and closing said door means, and means operable by said door switch means for further modifying the intervals between defrost periods provided by said timer means.

6. Refrigeration apparatus according to claim 2, and further characterized by the inclusion of door means for said cabinet lstructure and door switch means operable in response to opening and closing said door means, and means operable by said door switch means for further modifying the intervals between defrost periods provided by said timer means.

7. yIn a refrigerator', the combination of a cabinet with a door, an evaporator, a motor compressor, a condenser, and conduit means connecting said evaporator, said motor compressor and said condenser in series refrigerant ilow circuit, an electric defrost heater positioned for heat exchange with said evaporator, a thermostat responsive to temperatures within said refrigerator for cyclically energizing and deenergizing said motor compressor, a sofurce of energy, a dew point compensator heater of the electrical resistance type for said cabinet, switch means for selectively connecting and disconnecting said dew point compensator heater and said source of energy, a timer motor and a timer switch means operable thereby to provide either for energization of said motor compressor or for energization of said defrost heater, means for connecting said timer motor to said source of energy through said thermostat during operation of the compressor in the course of a normal refrigeration period, and means for connecting said timer motor to said source of energy continuously through said selector switch when the dew point compensator heater is energized.

8. A refrigerator according to claim 7 and further characterized by the inclusion of a door switch operable to connect said timer motor to said source of energy when said timer switch means is conditioned to provide for energization of said motor compressor.

9. A refrigerator according to claim 7, and further characterized in that said timer motor is of the heat motor type having an electrical resistance heater as the heat source, and by the inclusion of an electrical resistor connectible in series electrical circuit with said resistance heater and said thermostat, whereby said timer motor operates at a slower rate when said selector switch is in a position deenergizing said dew point compensator.

References Cited UNITED STATES PATENTS 3,460,352 8/1969 Lorenz 62-155 MEYER PERLIN, Primary Examiner U.S. Cl. X.R. 

